1. Field of the Invention
The invention relates to improvements in techniques for forming felts, particularly thick felts sucn as those intended for heat and sound insulation.
2. Background of the Prior Art
Conventionally, the formation of felts from fibers carried by a stream of gas is carried out by passing this gaseous current through a perforated receiving conveyor which retains the fibers. To fix the fibers, a binder is sprayed onto the fibers during the course of their trajectory towards the receiving conveyor. This binder is then hardened, for example, by a heat treatment.
This technique is used particularly in the production of mineral fiber felts. Due to the importance of this type of production, we will refer hereinafter to the formation of fibers of glass materials. Nevertheless, the improvements according to the invention can be applied to all felt-making methods, whether the fibers are mineral or organic.
One of the difficulties encountered in the preparation of these felts is connected with the uniform distribution of fibers over the whole of the felt. The current of gas carrying the fibers ordinarily has a limited cross-section which is a function in particular of the fiber-producing apparatus. Also, the current of gas does not normally manage to cover the entire width of the conveyor and the fibers are not uniformly d1stributed as a result.
Various means have been proposed in order to improve the distribution of fibers on the conveyor. Among these means, one of the most useful in practice is of the type described in U.S. Pat. No. 3,134,145. This consists of passing the flow of gas carrying the fibers through a guide duct. This duct is mobile and an oscillatory movement is imparted to it in order alternately to direct the flow of gas from one edge to the other of the fiber-receiving conveyor.
By this means, if the conditions of use are suitably chosen, the fibers become deposited over the full width of the conveyor.
In prior art techniques which employ an oscillating duct, as in U.S. Pat. No. 3,134,145, the movement is communicated by a connecting rod fixed on the one end to the duct and on the other to a crank or a disc to which a rotary movement is imparted according to an axis at right-angles to the axis of the connecting rod.
These prior art apparatuses furthermore comprise mechanical regulating means, for example means for regulating the length of the connecting rod, generally via the point of attachment of the connecting rod on the crank or disc, which make it possible respectively to determine the median direction and the amplitude of the oscillations communicated to the duct. Although these devices do on the whole function in a satisfactory manner, adjusting them while they are working is delicate insofar as such adjustment has to be carried out on moving mechanisms. The method of regulation proposed in these devices does not lend itself to automation.
The object of the invention is to provide an improved technique for the distribution of fibers in the felts produced.
It is a particular object of the invention to allow the distribution to be modified during the course of operation.
Another object of the invention is to ensure that modification of the distribution of fibers is carried out automatically according to variations in the distribution of fibers measured continuously on the felts produced.